1. Field of the Invention
This invention relates to gas flow in cryogenic deflashing machines, and more particularly to a media-assisting pressurized gas flow system preferably using dry gaseous nitrogen to propel shot blast media throughout the cryogenic deflashing process and chamber.
2. Description of the Related Art
Cryogenic deflashing is the process by which plastic or metal parts are cooled to low temperatures using cryogenic gases in order to remove flashing, burrs, and other thin structural imperfections with controlled impact collisions. Flashing is the term used for material used in a molding process that is extraneous to the part involved. As an example, when rubber, plastic, or metal components are cast in bulk, several pieces will be cast at the same time through the same mold in a detachably connected manner. This connected manner is temporary so that the individual parts are usually removed from a central holding stem. As molds often have two halves to them, extraneous material often extrudes into the seam between the two molds to create flashing.
This flashing is easily made brittle when subjected to cryogenic temperatures. Consequently, when flashing is so embrittled, it easily shatters and fragments to leave behind the part or component of interest. Although the part or component is also subject to cryogenic temperatures, the accompanying structure is generally sufficiently stronger and able to withstand the cryogenic and controlled impact collision process.
Taking advantage of this feature of flash, burrs, and other thin structures, cryogenic deflashing machines often use liquid and gaseous nitrogen in conjunction with a rotating foramenous chamber in order to break off the flashing and separate it from the desired part or component. As some parts have flashing in interior spaces, the mere tumbling of the parts against one another only removes the exterior flashing. Consequently, additional impacts or stress must be imposed upon such interior flash. It is known in the art to use impeller throw wheels in conjunction with polycarbonate plastic blasting shot in order to provide the necessary additional impacts to clear flashing, burrs, etc. from interior portions of the parts.
Such impeller driven systems often operate on the order of thousands of rpms and may require the associated cryogenic deflashing machine to use tens to hundreds of pounds of blasting shot media.
Consequently, it would be an advantageous development in the art to provide a system by which the flow of the media through the system could be assisted in a useful manner, preferably reducing the amount of shot necessary. Additionally, such a media assist system preferably maintains the interior confines of the cryogenic deflashing machine in a dry condition as water ice is easily formed (as the temperatures drop well below the freezing point of water) and formation of ice tends to block the free flow of media through the system.
Two examples of cryogenic deflashing machines arise in U.S. Pat. No. 4,979,338 issued to Schmitz, II et al. on Dec. 25, 1990 and U.S. Pat. No. 5,676,588 issued to Frederick et al. on Oct. 14, 1997. Both of these patents describe media assist systems of different sorts. The Schmitz, II et al. '338 patent uses the exhaust from a pneumatic motor to pull the media into the impeller housing chamber by venturi effect. Shop air is used to drive a pneumatic motor. As mentioned above, such shop air may carry water vapor even though it has been subject to desiccation or the like.
In the Frederick et al. '588 patent, a blower system is used to carry the media from a media bin to the throw wheel assembly.
Consequently, further advancements in the art remain to be made with respect to the flow of blast shot media throughout the distribution system present and a cryogenic deflashing machine. Such media must flow through the machine as the media must controllably collide with the parts to be deflashed, then leave that area in order to leave the blasted and deflashed parts free from extraneous material such as the blast shot media.